1. Field of the Invention
The present invention relates to a method of forming a metal line, and more particularly to a method for forming a reliable line.
2. Discussion of the Related Art
As information society develops, so does the demand for various displays. Recently, many efforts have been made to research and develop various types of flat display panels, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electroluminescent Display (ELD), Vacuum Fluorescent Display (VFD), and the like. Some of these flat display panels are already in use as displays in many different types of equipment. Typically, the LCD type of flat panel display is widely used as a substitution for the Cathode Ray Tube (CRT) for a mobile image display because of the characteristics or advantages of high quality image, lightness, shallow depth, compact size, and low power consumption. The LCD is also applicable for use in devices that receive video signals for display, such as television, computer monitor, and the like. However, in order to use an LCD device as a general display device in various fields, the LCD device should realize a high quality image at a high resolution, have high brightness and a wide screen as well as maintain the characteristics of lightness, shallow depth, compact size, and low power consumption.
An LCD device includes a liquid crystal display panel for displaying an image and a driving unit for applying a driving signal to the liquid crystal display panel. The liquid crystal display panel includes upper and lower substrates bonded to each other. A liquid crystal layer is in a space between the upper and lower substrates, which are both formed of glass. The lower substrate is also known as the Thin Film Transistor (TFT) substrate and upper substrate is also known as the color filter substrate.
A plurality of gate lines is formed on the lower substrate in one direction to leave a predetermined interval between each other. A plurality of data lines is arranged in another direction perpendicular to the gate lines to leave a predetermined interval between each other. A plurality of pixel electrodes is formed in a matrix structure within pixel areas defined between adjacent gate and data lines that cross over each other. A thin film transistor is provided in each of the pixel areas. The thin film transistor of each respective pixel area is switched by a signal of a gate line to transfer a signal from a data line to the pixel electrode of the respective pixel area.
A black matrix layer is formed on the upper substrate for cutting off light transmission through the upper substrate except where pixel areas are located. An RGB color filter layer for realizing colors is positioned adjacent the black matrix layer. A common electrode for creating vertical electric field is formed on the RGB color filter layer. In the alternative, the common electrode can be formed on the lower substrate if the device is a horizontal electric field type liquid crystal display device.
The upper and lower substrates are bonded to each other using a sealant while being separated from each other by spacers. The liquid crystal layer is positioned within the space surrounded by the sealant between the upper and lower substrates. The above-constituted general liquid crystal display device includes various electrode terminals and lines inside. For example, the various electrode terminals and lines include source/drain/gate electrodes of thin film transistors (TFTs) used as switching devices inside the liquid crystal cells, data lines for applying video data signals to the liquid crystal cells, gate lines for applying scan signals, and pixel/common electrodes for applying an electric field across the liquid crystal layer.
A method of fabricating such a liquid crystal display device includes a process of forming a TFT pattern by sputtering and patterning materials that are used as a gate or source/drain electrodes. For example, a gate forming process includes cleaning a substrate, depositing a gate layer by sputtering, performing a photolithographic process to form a mask on the gate layer, wet etching the gate layer using the mask to etch away the unwanted material, and removing the mask. In this case, the photolithographic process is carried out by coating a photoresist, exposing the photoresist with UV radiation and developing the photoresist such that the desired pattern is covered by the photoresist prior to the wet etch. In another example, the source/drain forming process is carried out by depositing a source/drain layer by sputtering, performing a photolithographic process to form a mask on the source/drain layer, wet etching the source/drain layer using the mask to remove unwanted material, and removing the mask. The photolithographic process of the source/drain forming process is similar to that of the gate forming process. However, in such a deposition process, the gate or source/drain electrode may not be deposited with a sufficient consistency or thickness to manufacture a reliable conductive metal line. A reliable conductive metal line is a line that does not have open-circuits or hot spots of high resistance that can later bum or separate into an open-circuit.
A method of forming a metal line according to the related art is explained by referring to the attached drawings as follows. FIG. 1 illustrates a diagram of sputtering according to the related art. Referring to FIG. 1, a metal 102 to be deposited is positioned on a backing plate 101. An Ar plasma 103 is generated in a chamber. The Ar plasma 103 causes Ar atoms to collide with the metal 102 such that atom clusters of the metal 102 are knocked off and are coated onto a substrate 100. In this case, the chamber pressure in the chamber for the Ar plasma is at least 0.8 Pa. The line degradation for manufacturing a metal line at pressures of 0.8 Pa or greater can be at least several tens of percentage points.
FIGS. 2A to 2C illustrate cross-sectional views of forming a metal line according to the related art. Referring to FIG. 2A, a metal 120 is deposited on a substrate 100 by sputtering. Referring to FIG. 2B, the metal is exposed to the atmosphere. As a result, an organic material 121 adheres to the exposed metal 120. The organic material 121 does not uniformly adhere to the metal 120, thus the surface of the metal 120 having the organic material 121 adhered thereto is uneven. Referring to FIG. 2C, a photoresist 130 is coated on the metal 120 having the organic material 121 adhered thereto. In this case, the organic material 121 inhibits the photoresist 130 from directly adhering to the metal 120, which causes the formation of unreliable or open-circuited metal lines. More particularly, the etchant used in the wet etch to etch away the unwanted metal also penetrates between the photoresist 130 and the organic material 121. Thus, the desired metal line is also etched or degraded.
Line degradation can cause either unreliable or open-circuited metal lines. For example, line degradation can be to the point where a line becomes an open-circuit. In the alternative, line degradation can cause hot spots or regions along the line having a high resistance. Accordingly, line degradation can hamper or prevent the operation of a device.